The present invention pertains to an air lock for introducing workpieces to and/or removing them from atmospherically separated chambers with at least one transfer channel connecting the chambers.
Air locks of this class are known, for instance, from German Patent Application No. P 27 47 061. This conventional air lock serves to introduce endless carrier belts which are to be coated in a vacuum chamber by means of the air lock from the surrounding outer area having normal pressure into the coating chamber and removing them from the coating chamber after the coating process is finished. The pressure difference between the external atmospheric pressure and the usual vacuum pressure for vacuum-supported coating processes of at most 10xe2x88x921 mbar is maintained over a pressure stage path which features several shutters arranged in succession, through which the carrier belt is guided. Essential elements of these so-called belt transfer channels, which bridge the pressure difference with respect to the pressure in the actual coating chamber, are the shutters constructed as slits or gaps, which oppose a significant resistance to air flow, so that the desired pressure differential is possible using vacuum pumps.
In order to guarantee a sufficient atmospheric separation between the coating chamber and the outer chamber, it is necessary to adapt the shutters to the profile of the carrier belt in order to prevent the passage, for instance, of air into the coating chamber.
Another restriction of such an air lock is that the carrier belt itself is necessary for the sealing function of the shutters, so that it is necessary that the carrier belt be led through the air lock exclusively in an endless manner in order to prevent a rise of pressure in the coating chamber. This disadvantageously very sharply restricts the use of this known air lock in regard to the workpieces that can be transported through the transfer channel.
An object of the present invention is to create an air lock for this technology that permits a continuous transport of workpieces between two chambers, the two chambers being atmospherically separated from one another, but does not display the disadvantageous restrictions mentioned above.
The above and other objects of the invention can be attained in that the atmospherically separated chambers are connected by a transfer channel, in which at least one lock chamber accommodating the workpiece to be transferred is arranged movably between the chambers, and wherein the lock chamber features an opening for loading and unloading the workpieces and at least one sealing device, by means of which the lock chamber interior is atmospherically sealed off from the adjacent spaces.
The air lock according to the invention is suited to transfer the workpieces between chambers with identical atmospheric pressure as well as between chambers which have different atmospheric pressures.
A particular advantage results if one of the chambers has normal atmospheric pressure and the other chamber has a negative atmospheric pressure. Since the negative pressure is maintained during the transfer of the workpieces into or out of the negative pressure chamber, the coating processes performed in the negative pressure chamber requiring a vacuum pressure can be performed continuously. The exposure to air and subsequent evacuation of the vacuum chamber, in particular, for introducing or removing the workpieces to be treated, are not necessary according to the invention. With the air lock according to the invention it is thus possible to transport the workpieces into the chamber having atmospheric characteristics differing from the exterior space or out of it in an efficient manner which is favorable in terms of cost and time.
In practice, a vacuum-coating chamber which had a negative atmospheric pressure of at most 10xe2x88x923 mbar during the coating process was successfully loaded by means of the air lock according to the invention with workpieces to be coated from the exterior space at normal pressure, or unloaded with the workpieces (substrates) that had been coated in the vacuum-coating chamber. Representative workpieces are beverage containers but any suitable workpiece is contemplated herein.
A particularly simple design of the air lock results wherein the air lock comprises a carrousel lock formed essentially of a carrousel housing and a lock chamber wheel seated so as to be able to rotate in the carrousel housing. Individual lock chambers whose individual openings are accessible in the radial direction are inserted or formed into the lock chamber wheel on the periphery. The carrousel housing constituting the transfer channel has sealing devices at its periphery which make sealing contact with the inside wall of the transfer channel during material transport, whereby the individual chambers are atmospherically separated from one another and, for instance, from the atmospheric spaces having different atmospheric pressures. It has proven to be of advantage to adapt the individual lock chambers in terms of pressure via a pressure stage during their transition from the space under higher pressure to the space under lower pressure, in order to prevent the introduction of atmospheric gas into the vacuum chamber. To this end, it is provided that the lock chambers be evacuated by means of suitable pumps, for instance, vacuum pumps. The transfer channel is also connected via several suction connectors to vacuum pumps. The design of the vacuum pumps is selected such that the atmospheric pressure in the transfer channel decreases or increases continuously or step by step. The individual, mutually adjacent transfer channels thus exhibit different pressures as a function of their position.
The sealing devices arranged between lock chambers and the inside wall of the transfer housing are formed of slide sealing elements which make a seal on the periphery of the lock chamber wheel and of radial gaskets which are arranged continuously and, for instance, in one piece as a gasket belt running peripherally on the transfer channel rim and prevent the passage of atmospheric air in the radial direction of the transfer channel wheel. The gasket unit is advantageously constructed as a dry gasket, which avoids the use of lubricants. To this end, it is proposed to employ slides of a wear-resistant elastic synthetic polymeric material, for instance, Teflon(copyright).
Loading devices which are preferably arranged diametrically to one another and adjacent to the lock chamber wheel in the atmospherically mutually separated spaces are provided for loading and unloading the lock chambers. These loading/unloading devices each have gripping devices which, for instance, convey the untreated substrates into the lock chambers for transfer into a treatment chamber and which convey the treated substrates into the individual lock chambers for outwards transfer.
Furthermore, it is proposed to employ the air lock according to the invention for transferring substrates to be coated by means of a vacuum-coating process into/out of a coating chamber having a coating source. Suitable coating sources are known vaporization sources and/or sputtering cathodes for generating a cloud of vaporized and/or sputtered coating material for deposition onto the substrates to be coated. The substrates can include plastic containers such as bottles, on the outer wall of which a blocking layer which is optically transparent but impervious to the passage of gases or fluids is deposited. To this end, silicon-containing source material is vaporized and/or sputtered by means of the vaporization or sputtering cathode source and then reacted with a reaction gas containing oxygen which is introduced into the coating chamber, reacts and deposits as an SiO2 layer on the plastic containers.